The present invention relates to a method for improving surface properties of a shaped article of a synthetic resin. More particularly, the invention has an object to impart a shaped article of a synthetic resin with an improved antistatic performance with durability and permanency by the treatment of the surface with low temperature plasma.
Needless to say, shaped articles of synthetic resins are widely used in almost all fields of not only industrial but also in household uses by virtue of their advantages that they can be supplied with great inexpensiveness due to the easiness of their manufacturing and that they have various excellent properties including electric insulation. As a reflection of their high electric insulation, however, shaped articles of synthetic resins generally have a high surface resistivity with low dielectric loss so that troubles are often caused by the accumulation of static electricity on the surface. For example, beautifulness in the appearance of a synthetic resin shaped article is rapidly lost by the deposition of dusts and dirts on the surface as attracted by the static charge. Highly charged synthetic resin shaped articles sometimes cause an electric shock to human body coming into contact therewith or generate spark discharge which may influence electronic circuits to produce noises.
Several methods have been proposed to prevent- accumulation of static electricity on the surface of a synthetic resin shaped article. The methods of antistatic treatment hitherto proposed include, for example, a method in which an electroconductive powdery material such as a metal powder and carbon black is incorporated into the synthetic resin prior to shaping of the resin into articles, a method in which a thin surface film of a metal is formed on the surface of the shaped article by sputtering, vacuum vapor deposition and the like techniques, a method using a surface active agent which is either incorporated into the resin prior to shaping or applied to the surface of the shaped article to form a coating film thereon, a method of the treatment of the surface with a chemical such as an acid or with a flame, a method in which hydrophilic functional groups are introduced on to the surface of the shaped article by the grafting reaction induced with actinic rays, e.g. electron beams, ultraviolet light and ionizing radiations, and others.
Unfortunately, none of the above mentioned prior art methods is sufficiently effective to impart antistatic performance to the surface of a synthetic resin shaped article or, if not ineffective at all, the properties of the synthetic resin is greatly degraded by the antistatic treatment or the method cannot be performed practically due to the expensiveness of the treatment or the inapplicability of the method for the mass treatment of a large quantities of the synthetic resin shaped articles.